The fact that we don't feel narced doesn't mean we are not affected. Sometimes we feel it at 60 feet, sometimes at 150 feet. Feeling is a very subjective sensation. NN is well researched and documented, through objective studies of individual performance. Before we even get to the "weird" point, our capability to perform is being reduced. And that starts right from 5 feet under and gets more and more severe as we go deeper. Regardless of if we feel it or not.